Devices for detecting vehicles or other physical objects located ahead of or to the rear of an operating vehicle using laser radar have been proposed in the past. For example, in Japanese Patent Application Kokai No. Hei 06-150196, a method is described. Moving physical objects located ahead of the vehicle mounting the detection system are detected by laser radar. Information concerning the detected moving physical objects is stored in a memory, and control such as a tracking operation, etc., is performed. Specifically, if a moving physical object stored in the memory is not detected in the current detection process, the information concerning the moving physical object is retained in the memory as a detection error due to some cause until non-detection occurs a predetermined number of times. Then, when such a failure has occurred a predetermined number of times, the information concerning this moving physical object is deleted from the memory.
However, in such a method, if the number of times that a physical object that is not detected is retained without being deleted from the memory (i.e, the number of times of interpolation) is increased, the following problem arises. Namely, although such an increase makes it possible to continue the recognition of external physical objects in a more continuous manner, the interpolation treatment creates erroneous recognition which makes it appear as though an external physical object is present in the detection area of the system even when the external physical object has moved out of the detection area. Conversely, if the number of times of interpolation is decreased, the recognition of physical objects becomes intermittent as a result of detection error by the system.